Saitama is a hero who only became a hero for fun.

After three years of "special training," he's become so strong that he's practically invincible. In fact, he's too strong—even his mightiest opponents are taken out with a single punch. Alongside Genos, his faithful disciple, Saitama performs his official hero duties as a member of the Hero Association.

One day, monsters claiming to be from the Monster Association suddenly appeared, taking a child of the Hero Association executive hostage. The S-class heroes gather and plan a raid on the Monster Association hideout to rescue the hostage. Meanwhile, Garou, a "human monster" who was taken by the Monster Association during a battle with the heroes, awakens in the Monster Association hideout.

Source: Viz

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Prequel: One Punch Man (2019)
Sequel: One Punch Man (2027)